Hess's Law Worksheet
1.	Calculate ∆H for the reaction: C2H4 (g) + H2 (g) → C2H6 (g), from the following data. 
C2H4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2O (l)	∆H = -1411. kJ	
C2H6 (g) + 3½ O2 (g) → 2 CO2 (g) + 3 H2O (l)	∆H = -1560. kJ	
H2 (g) + ½ O2 (g) → H2O (l)	∆H = -285.8 kJ	
2.	 Calculate ∆H for the reaction 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g), from the following data.
N2 (g) + O2 (g) → 2 NO (g)	∆H = -180.5 kJ	
N2 (g) + 3 H2 (g) → 2 NH3 (g)	∆H = -91.8 kJ	
2 H2 (g) + O2 (g) → 2 H2O (g) 	∆H = -483.6 kJ	
3.	Find ∆H for the reaction 2H2 (g) + 2C (s) + O2 (g) → C2H5OH (l), using the following thermochemical data. 
C2H5OH (l) + 2 O2 (g) → 2 CO2 (g) + 2 H2O (l)	∆H = -875. kJ	
C (s) + O2 (g) → CO2 (g)	∆H = -394.51 kJ	
H2 (g) + ½ O2 (g) →  H2O (l)	∆H = -285.8 kJ	
4.	Calculate ∆H for the reaction CH4 (g) + NH3 (g) → HCN (g) + 3 H2 (g), given: 
N2 (g) + 3 H2 (g) → 2 NH3 (g)	∆H = -91.8 kJ	
C (s) + 2 H2 (g) → CH4 (g)	∆H = -74.9 kJ	
H2 (g) + 2 C (s) + N2 (g) → 2 HCN (g)	∆H = +270.3 kJ	
5.	Calculate ∆H for the reaction 2 Al (s) + 3 Cl2 (g) → 2 AlCl3 (s) from the data.
2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g)	∆H = -1049. kJ	
HCl (g) → HCl (aq)	∆H = -74.8 kJ	
H2 (g) + Cl2 (g) → 2 HCl (g)	∆H = -1845. kJ	
AlCl3 (s) → AlCl3 (aq)	∆H = -323	

6.	Calculate ∆H H for the reaction 4 NH3 (g) + 5 O2 (g) →  4 NO (g) + 6 H2O (g), from the following data. 
N2 (g) + O2 (g) → 2 NO (g)	∆H = -180.5 kJ	
N2 (g) + 3 H2 (g) → 2 NH3 (g)	∆H = -91.8 kJ	
2 H2 (g) + O2 (g) → 2 H2O (g) 	∆H = -483.6 kJ	

7.	
Find ∆H H° for the reaction 2H2(g) + 2C (s) + O2 (g) →  C2H5OH (l), using the following thermochemical data. 
C2H5OH (l) + 2 O2 (g) → 2 CO2 (g) + 2 H2O (l)	∆H = -875. kJ	
C (s) + O2 (g) → CO2 (g)	∆H = -394.51 kJ	
H2 (g) + ½ O2 (g) → H2O (l)	∆H = -285.8 kJ	

8.	Calculate ∆H H for the reaction CH4 (g) + NH3 (g)  HCN (g) + 3 H2 (g), given: 
N2 (g) + 3 H2 (g) →2 NH3 (g)	∆H = -91.8 kJ	
C (s) + 2 H2 (g) → CH4 (g)	∆H = -74.9 kJ	
H2 (g) + 2 C (s) + N2 (g) → 2 HCN (g)	∆H = +270.3 kJ	
9.	From the following enthalpies of reaction,
4HCl (g) + O2 (g) → 2H2O (l) + 2Cl2 (g)  		∆H= - 202.4 kJ
½  H2 (g) + ½  F2 (g) → HF (g)  			∆H = - 600.0 kJ
H2 (g) + ½  O2 (g) → H2O (l)   			∆H= - 285.8 kJ

find ∆Hrxn for 2HCl (g) + F2 (g) → 2HF (g) + Cl2 (g).
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10.	From the following enthalpies of reaction,
CaCO3 (s) → CaO (s) + CO2 (g)  			∆H =  +178.1 kJ
CaO (s) + H2O (l) → Ca(OH)2 (s)  			∆H = - 65.3 kJ
Ca(OH)2 (s)  → Ca2+_(aq) + 2 OH- (aq) 		∆H = -16.2 kJ

calculate ∆Hrxn for
Ca2+ (aq) + 2OH- (aq) + CO2 (g) → CaCO3 (s) +  H2O (l)
11.	*0 Given that
S (s) + O2 (g) → SO2 (g)		 		∆H= -296.8 kJ
S (s) +  O2 (g) → SO3 (g)		 		∆H= -395.6 kJ
determine the enthalpy change for the decomposition reaction 2 SO3 (g) → 2 SO2 (g) + O2 (g).

12.	Aluminum reacts vigorously with many oxidizing agents.
For example,
4 Al (s)+  3 O2 (g) → 2 Al2O3 (s)  			∆H= -3352 kJ
4Al (s) + 3 MnO2 (s) → 3Mn (s) + 2 Al2O3 (s)		∆H= -1792 kJ
Use this information to determine the enthalpy of formation of MnO2 (s).

13.	Given that
2 H2 (g) + O2 (g) → 2 H2O (l)			∆H= -571.6 kJ
C3H4 (g) + 4 O2 (g) → 3 CO2 (g) + 2 H2O (l) 		∆H= -1937 kJ.
C3H8  (g) + 5 O2 (g) → 3CO2 (g) + 4 H2O (l)		∆H= -2220 kJ.
determine the heat of the hydrogenation reaction
C3H4 (g) + 2 H2 (g) → C3H8 (g)

14.	Determine the heat of formation of liquid hydrogen peroxide at 25°C from the following thermochemical equations.
H2 (g) + ½ O2 (g) → H2O (g) 				∆H0 = -241.82 kJ
2 H (g) + O (g) →  H2O (g) 			∆H0 = -926.92 kJ
 	2H (g) + 2O (g) → H2O2 (g)			∆H0= - 1070.60 kJ
2 O (g) → O2 (g) 					∆H0 = - 498.34 kJ
H2O2 (l)  → H2O2 (g)				∆H0 = 51.46 kJ